Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $59.41   8.211%   $64.2882   $64.29   $64.30   $64.30  
  Purchase #2 $150.28   3.152%   $155.0168   $155.02   $155.00   $155.00  
  Purchase #3 $7.39   8.581%   $8.0241   $8.02   $8.00   $8.00  
  Purchase #4 $69.43   5.429%   $73.1994   $73.20   $73.20   $73.20  
  Purchase #5 $123.82   4.398%   $129.2656   $129.27   $129.25   $129.30  
  Purchase #6 $101.46   8.396%   $109.9786   $109.98   $110.00   $110.00  
  Purchase #7 $117.74   8.809%   $128.1117   $128.11   $128.10   $128.10  
  7 purchase totals = $629.53       $667.8844   $667.89   $667.85   $667.90